Microorganisms such as algae are constantly exposed to harsh environmental conditions during their life cycle. The harsh environmental conditions include abiotic stresses such as ultraviolet radiation (UV), salinity, light, unfavorable temperature, alkalinity, nutrient limitation, oxidative stress, senescence, sulfur deficiency, carbon deficiency, nitrogen use inefficiency and the like. Biotic stresses include infection by virus, bacteria, fungus or other stress causing pathogens. These conditions pose a constant threat to the DNA integrity of these microorganisms and cause damage to their DNA, such as modified bases, mispaired bases, intrastrand crossbinding, interstrand crossbinding, pyrimidine dimers, single stranded breaks and double stranded breaks (DSBs). This consequently leads to cell death, thereby preventing the survival of these microorganisms in harsh environments. In order to overcome stress, these microorganisms are required to physiologically adapt themselves to such harsh environmental conditions. This may lead to loss of the unique traits of interest in these organisms. The low survival capacity and loss of unique traits of interest in these organisms are the major difficulties in exploiting their capabilities for industrial purposes.
The repair of DNA double strand breaks (DSBs) is essential to maintain the integrity of the genome. Un-repaired or improperly repaired DNA damage may result in genomic instability and eventually in cell death.
Many proteins are necessary for such DNA DSB—repair. One such important protein is Rad52 protein, which is necessary for accurate repair of DSBs and is highly conserved among eukaryotes, including animals, fungi and yeast. It also plays an auxiliary role with the replication protein A (RPA) in the action of Rad51 protein. Furthermore, Rad52 protein has an annealing activity and promotes the formation of D-loops in super helical DNA.
Disruption of RAD52 gene may cause severe recombination phenotype including extreme X-ray sensitivity, increased chromosome loss and failure to produce viable spores. Research on Rad52 mutants in Saccharomyces cerevisiae has revealed a critical role of Rad52 protein in double-strand break repair and meiosis. It has been revealed that in Saccharomyces cerevisiae, homologous recombination provides a major mechanism for eliminating DNA double-stranded breaks which may be induced by ionizing radiations or may be associated with injured DNA replication forks; and Rad52 protein plays a fundamental role in homologous recombination pathway and DNA double strand break repair.
WO2003089573 suggests a method of identifying compounds that induce a DNA repair pathway and/or inhibit retroviral cDNA integration into a host genome.
US20040111764 suggests an expression cassette comprising a meiotically active promoter operably linked to a polynucleotide encoding a recombinational DNA repair polypeptide or its fragment, which is capable of stimulating plant meiotic recombination when expressed into RNA and/or said polypeptide.
However, these conventional methods are typically incapable of enhancing the survival capacity of microorganisms along with enhanced biomass synthesis and simultaneously maintaining their genomic integrity in an effective and efficient manner, wherein confirmed stable transgene integration is being achieved. Additionally, some conventional methods employ a large number and/or quantity of chemicals in order to facilitate enhanced biomass synthesis.
Therefore, there exists a need to develop an efficient and effective method for enhancing the biomass synthesis capacity of a microorganism.